The invention relates to the preparation of unsaturated esters and to the conversion of these esters to polyunsaturated compounds. Prior art methods for preparing unsaturated esters by reacting an olefin and an acid were adversely affected by small amounts of water and required expensive catalysts. Accordingly, it is an object of the present invention to provide a new and improved process for preparing unsaturated esters. Another object is to provide new catalysts for this reaction. Still another object is to provide a new and improved method for preparing polyunsaturated compounds.